1. Field of the Invention
The present invention relates to an antenna array receiver for performing reception by use of an antenna array.
The present invention also relates to a method of correcting a phase shift amount of a receiving signal.
2. Description of the Related Art
Conventionally, in order to perform directional reception by use of an antenna array, a receiver is designed so as to perform reception while maintaining the phase difference at the antenna terminals among receiving signals from a plurality of antennas.
FIG. 1 shows an example of the antenna array receiver.
First, receiving signals S1 and S2 at antennas 1301 and 1302 are amplified by receiving amplifiers 1303 and 1304. Then, the signals are multiplied by a signal from an oscillator 1307 by mixers 1305 and 1306 and a lower-frequency signal is extracted by band-pass filters (BPFs) 1308 and 1309. At quadrature demodulators 1310 and 1311, quadrature demodulation is performed by use of a signal from an oscillator 1312, and in-phase components S11 and S21 and quadrature components S12 and S22 are output. These output signals are converted into digital values by A/D converters 1313, 1314, 1315 and 1316, and output to an adaptive antenna array receiving circuit 1317.
At RSSI detect circuits 1318 and 1319, the lower-frequency signal extracted by the BPFs 1308 and 1309 is monitored and the levels of the receiving signals are detected. In accordance with the receiving signal levels, the gains of the receiving amplifiers 1303 and 1304 are controlled by gain control circuits 1320 and 1321.
In wireless communication, the levels of receiving signals vary with time. Particularly, in a mobile communication environment, the levels of receiving signals largely vary in a short period of time due to fading, variation in propagated distance and shadowing because of buildings and the like.
In the above-described conventional antenna array receiver, by controlling the gains of the receiving amplifiers 1303 and 1304 by the RSSI detect circuits 1318 and 1319 and the gain control circuits 1320 and 1321, the receiving signal levels are corrected to thereby optimize the input to the A/D converter.
However, generally, the phase shift amount of a receiving amplifier varies according to the gain thereof. The amount of the phase variation differs among receiving amplifiers. The phase shift amount varies according to the frequency and the temperature of the receiving amplifier. The electric length, i.e. the length converted into a wavelength, varies according to the frequency.
For this reason, according to the above-described conventional configuration, the phase difference at the antenna terminals between the receiving signals of the antennas cannot be maintained constant.